In an electrophotographic image forming apparatus, a structure is known in which elements such as a photosensitive drum and a developing roller as rotatable members contributable to image formation are integrated as a cartridge, and the cartridge can be mounted to and dismounted from the main assembly of the image forming apparatus (hereinafter referred to as apparatus main assembly). Here, in order to rotate the photosensitive drum in the cartridge, it is desirable to transmit the driving force from the main assembly of the device. At that time, it is known that a coupling member on the cartridge side is engaged with a driving force transmission portion such as a drive pin on the side of the main assembly to transmit the driving force.
Here, a structure of a cartridge that is removable in a predetermined direction substantially perpendicular to the rotation axis of the photosensitive drum is known. Japanese Laid-open Patent Application No. 2008-233867 discloses a structure in which a coupling member provided at the end portion of the photosensitive drum can incline relative to the rotation axis of the photosensitive drum. it is known that by doing so, a coupling member mounted on a cartridge is engaged with a driving pin provided in the main assembly of the apparatus, and a driving force is transmitted from the apparatus main assembly to the cartridge